rodshaped

Rod-shaped describes objects with a cylindrical, elongated body and a roughly circular cross-section. In biology the term is most commonly applied to cells and microorganisms that adopt this cylindrical geometry, especially bacteria. When used in microbiology, rod-shaped bacteria are often referred to as bacilli (singular: bacillus). The descriptor is purely morphological and does not denote a single taxonomic group.

In bacteria, rod-shaped cells can be straight or curved and may occur singly or in arrangements such as chains. Typical dimensions vary by species and growth conditions, but cells are commonly several micrometers long and about one micrometer in width. The shape can influence surface area to volume ratio, nutrient uptake, motility, and the formation of biofilms. Some bacteria are strictly rod-shaped, while others are pleomorphic and can assume multiple shapes under environmental stress or during different life cycle stages. The term bacillus is often used informally to refer to rod-shaped bacteria, but it is also the name of a genus, so context matters to avoid confusion.

Rod-shaped geometry is also a key descriptor in materials science for elongated particles called nanorods and microrods. These rod-like nanomaterials exhibit anisotropic properties, with direction-dependent optical, electronic, and catalytic behaviors. Synthesis methods include chemical routes and templating techniques, enabling control over aspect ratio, diameter, and surface functionalization.

See also: bacterial morphology, bacillus, nanorod, microrod.